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Daniel Hilst
7d52506a2d
The build lock is released in DESTROY, and perl does not run DESTROY when a signal
ends the process. A build stopped with SIGTERM or SIGINT therefore left its lock
directory behind, and the next build of that checkout died on
FATAL: another build of <path> already holds <dir> (held by [pid=NNNN])
naming a pid that had already exited. Nothing clears it but a person. One such
directory blocked an openSUSE target across three consecutive CI runs before anyone
looked at what the lock actually said.
buildrpms.pl has released its lock on cancellation for some time, through an END
block and an abort handler. This is the Debian builder catching up.
The order matters, and is the reason this is not simply an END block. The command in
flight is stopped BEFORE the lock is released: handing the checkout to a second build
while dpkg-buildpackage is still rewriting debian/changelog and debian/control in it
is worse than holding the lock a moment longer. The wait for that command is bounded,
so a subprocess that ignores the signal cannot hold the lock for ever either.
sh() now forks and execs rather than calling system(), because system() gives no pid
and a handler cannot stop what it cannot name. The child _exits rather than exits, so
it never runs the parent's END block and releases a lock the parent still holds.
The handler is installed by XCAT::BuildUtils::install_build_cancellation rather than
written inline in the builder, so a test can use the same wiring the builder uses. A
test that installs an equivalent handler of its own proves the helper works while
saying nothing about whether anything calls it -- the first version of this test did
exactly that, and passed with the wiring removed.
Release is idempotent: a signal handler and then DESTROY both reach it, and the
second must not remove a directory a LATER build has since taken.
builddebs_lock_cancellation.t terminates the holder, then takes the lock again, and
checks no build subprocess was orphaned. Verified by removing the wiring: assertions
9 through 12 fail, naming the leaked lock, the refused build and the stray process.
Signed-off-by: Daniel Hilst <392820+dhilst@users.noreply.github.com>